In various technical fields such as, for example, a display, a printing apparatus, precision measurement, precision processing, and information recording-reproduction, a micro electro mechanical system (MEMS) device which is manufactured by a semiconductor fabrication technology is actively researched. As the above described MEMS device, a MEMS scanner which is used for a scanning with a laser light is known. The MEMS scanner has a movable plate; a supporting frame which surrounds the movable plate; and a torsion bar which coupled the movable plate with the supporting frame such that the movable plates swings.
In the MEMS scanner, a force (for example, a force for twisting the torsion bar) is usually applied to the torsion bar to swing the movable plate. However, when the twisting force is applied to the torsion bar, the force is often applied to not only the torsion bar but also one portion or whole of the movable plate. The force which is applied to the movable plate results in a deformation of the movable plate.
However, the deformation of the movable plate results in a deformation of a mirror or the like which is disposed on the movable plate. The deformation of the mirror or the like is undesirable, because it results in a reduction of a precision of the scanning with the laser light. Therefore, a technology which forms a protruding rib on a surface of the movable plate (typically, a surface of the movable plate which is opposite to a surface on which the mirror is disposed) is proposed to suppress the deformation of the movable plate (namely, to maintain a flatness of the movable plate) (for example, refer to Patent Literatures 1 to 3.